1. Field of the Invention
The present invention relates to a carboxylic acid tertiary alkyl ester, specifically, a monocarboxylic acid tertiary alkyl ester and a dicarboxylic acid tertiary alkyl ester. It relates to a method for producing, for example, t-butoxycarbonyl substituted norbornene derivatives or decahydronaphthalene-2,6-dicarboxylic acid di-t-butyl esters, etc. easily on an industrial scale at a good yield ratio. Furthermore, in detail, the present invention relates to a method for producing a monocarboxylic acid monoester or a dicarboxylic acid diester of a tertiary alcohol, whose production is generally difficult, from a corresponding monocarboxylic acid or dicarboxylic acid and a tertiary alcohol in a single-step reaction process and at a high yield ratio.
2. Description of the Related Art
Conventionally, it is known that an esterification reaction of a carboxylic acid and an alcohol can be prepared by a method of direct esterification in the presence of an acid catalyst, a method for making a carboxylic acid react with an alcohol after halogenating it, or a method for interchanging an ester in the presence of an acidic catalyst or a basic catalyst. These esterification reactions easily proceed with a primary or secondary alcohol. With a tertiary alcohol, however, an esterification reaction does not proceed well due to steric hindrance caused by substituents. Because a dissociation reaction of an ester generated can easily occur due to unstable carbocations, the esterification does not proceed easily using esterification methods usually used; it is difficult, and the yield ratio is extremely low.
In recent years, carboxylic acid tert-alkyl esters attract attention in the electronic materials field. For example, tetracyclo[4,4,0,12,5,17,10]dodece-8-ene-3-carboxylic acid t-butyl esters of a t-butoxycarbonyl substituted tetracyclododecen class attract attention as a material for highly integrated circuits, particularly for a resist resin suitable for exposure in a vacuum ultraviolet ray region for ArF excimer lasers, etc.
Conventionally, as a method for producing a t-butoxycarbonyl substituted tetracyclododecen class, it is known that it can be obtained by the Diels-Alder reaction of a t-butylacrylate and a dicyclopentadiene class (K. D. Ahn J. Photopolym. Sci. Technol., Vol. 11, No.3, 499-503 (1998)).
Unlike a case where a t-butoxycarbonyl substituted norbornane class can be obtained easily at a high yield by the Diels-Alder reaction of a t-butylacrylate and a cyclopentadiene class, the above-mentioned production method using a t-butylacrylate as a raw material includes a problem in that the Diels-Alder reaction requires the conditions of a high reaction temperature of 180 to 200xc2x0 C. while applying pressure. For this reason, a carboxylic acid substituted tetracyclododecen class, which is generated with a butyl group being separated from a t-butoxycarbonyl substituted tetracyclododecen class generated from the reaction, is easily generated and there are cases where this can cause a side reaction. There are other problems that the yield ratio is low due to various by-products of a t-butoxycarbonyl substituted norbornane class generated and that precision distillation is required to obtain an object of high purity from a reaction product.
Consequently, in view of difficulties in producing carboxylic acid tertiary alkyl esters, e.g., the situation described above regarding the method for producing a t-butoxycarbonyl substituted tetracyclododecen class, an object of the present invention is to provide a method for producing carboxylic acid tertiary alkyl esters of high purity using a tertiary alcohol and carboxylic acids as raw materials, under conditions that are easily implemented on an industrial scale, at a high yield. Carboxylic acid tertiary alkyl esters here include monocarboxylic acid tertiary alkyl esters such as a t-butoxycarbonyl substituted tetracyclododecen class and a t-butoxycarbonyl substituted bicyclo-hept-ene and dicarboxylic acid di-tertiary alkyl esters such as decahydronaphthalene-2,6-dicarboxylic acid di-t-butyl esters.
According to the present invention, a method for producing a carboxylic acid tertiary alkyl ester expressed by chemical formula 1 is provided. The method is characterized in that an esterification agent possessing a monovalent acid group that is ester-interchangeable with a tertiary alcohol is added continually to a mixed fluid of a carboxylic acid and a tertiary alcohol in the presence of a catalyst.
R1(COOR2)nxe2x80x83xe2x80x83[Chemical formula 1]
wherein R1 indicates a hydrocarbon group; R2 indicates a tertiary saturated hydrocarbon group; n indicates a positive integer 1 or 2.